MXene Hollow Spheres Supported by a C–Co Exoskeleton Grow MWCNTs for Efficient Microwave Absorption

Highlights A hollow core–shell structure was constructed with C–Co as the exoskeleton to support the MXene and multiwalled carbon nanotubes (MWCNTs) endoskeleton, with MWCNTs growing toward the center of the sphere. A reflection loss of − 70.70 dB and an effective absorption bandwidth of 5.67 GHz were obtained when the thickness was only 2.04 mm. The powder filler ratio was only 15 wt%. The unique hollow core–shell structure enhanced multiple reflection and scattering losses. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-024-01326-3.


Supplementary Figures and Tables
Fig. S1 SEM image of PS@MXene@ZIF67 with incomplete MXene coating    Fig. S13 SEM images of a1 ZIF67, b1 PS@ZIF67, c1 MXene@ZIF67, and d1 PS@MXene before calcination.SEM images of a2 ZIF67-600, b2 PS@ZIF67-600, c2 MXene@ZIF67-600, d2 and PS@MXene-600 after calcination at 600℃.RL values corresponding to 1-5 mm thickness for samples a3 ZIF67-600, b3 PS@ZIF67-600, c3 MXene@ZIF67-600, and d3 PS@MXene-600.The remaining scales in the Figure are all 1 μm Figure S13 shows four sets of comparative experiments, in which factors such as sample ratio, preparation process, and reaction time before calcination were consistent with the parameters used for preparing the same product PMZ-2.The calcination temperature, holding time, and heating rate of the four groups of samples were consistent with the parameters for preparing HMCCo-2 under the same conditions.In addition, the method of preparing coaxial rings and the filler ratio are also consistent with the previous text.

Fig. S14 a1
Real and imaginary parts of complex dielectric parameters, a2 real and imaginary parts of complex permeability, and a3 dielectric loss tangent and magnetic loss tangent for ZIF67-600.b1 Real and imaginary parts of complex dielectric parameters, b2 real and imaginary parts of complex permeability, and b3 dielectric loss tangent and magnetic loss tangent for c1 Real and imaginary parts of complex dielectric parameters, c2 real and imaginary parts of complex permeability, and c3 dielectric loss tangent and magnetic loss tangent for MXene@ZIF67-600.d1 Real and imaginary parts of complex dielectric parameters, d2 real and imaginary parts of complex permeability, and d3 dielectric loss tangent and magnetic loss tangent for PS@MXene-600    S22 a1 Complex permittivity, a2 complex permeability and a3 RL curves at 5 wt% filler ratio.b1 Complex permittivity, b2 complex permeability and b3 RL curves at 10 wt% filler ratio.c1 Complex permittivity, c2 complex permeability and c3 RL curves at 15 wt% filler ratio.d1 Complex permittivity, d2 complex permeability and d3 RL curves at 20 wt% filler ratio As shown in the Fig. S22, with the increase of mass ratio, the real part of complex dielectric constant is increasing, and the electromagnetic wave absorption performance first increases and then decreases, and the minimum reflection loss value is minimized at 15 wt%, which is -70.70 dB.When the filler ratio reaches 20 wt%, the complex dielectric constant of the material increases dramatically.According to the free electron theory, an excessively high dielectric constant will result in more incident electromagnetic waves being reflected by the absorber, which is detrimental to the dissipation of electromagnetic waves.In summary, we believe that the dielectric constant and magnetic permeability of the material are maintained at an appropriate level at a filler ratio of 15 wt%, so we uniformly use a filler ratio of 15 wt% in our study.

Fig. S2
Fig. S2 Disperse HMCCo-2 in ethanol solution and sonicate for 15 minutes before taking TEM images.a Single carbon nanotube separated after ultrasound.b Elements mapping for single carbon nanotubes.c-e Single carbon nanotubes separated after ultrasound.f High resolution TEM images of carbon nanotube tips and Co nanoparticle

Fig. S15 a
Fig. S15 a The attenuation constant curves and b μ''(μ') -2 f -1 -Frequency curves of four samples.c |Zin/Z0|-value curves of four groups of samples at the corresponding thickness when RL value reaches the minimum

Table S1
List of instructions for preparing sample labels